Purification and dehydration of gases



Aug. 15, 1950 w. F. CHAPIN PURIFICATION AND DEHYDRATION 0F GASES Filed June 28, 1948 IN V EN TOR.

' .B 4&2

IQTfOINEY.

Patented Aug. 15 1950 umreo 1 PATENT oeeic PURIFWATIQN AND min-mic on r v "GASES? Williamdh Qhapin lWhittfer, oans, assfgnor to The Fluotflornoration Ltd Los Angeles, 'Califga. corporation of tl'z'rlifi'n'nia This. inventionhasvto, do: with, the-treatmentof gaseous mixtures,,notably natural and refineryhydrocarbon. gases, for. the. removal: of acidic im purities, such asv hydrogen sulfide and carbon; di-

' oxide, andalso moistureinitiallycontainedintthe gas. More particularly, the. invention. is, directed to improvements. in. the type, of. process. disclosed in Patent No. 2, 435,0B9,,i'ss11ed' January 27., 1948, on. Gas Purification andiDehydration. Rrocess? According to the McCartneyprocess tliegas.to be treated iscontacted with a first treatinglsolution containing an acid" gas absorbent; and. the solution is continuously circulatedithrough vafirst heating zone or still to regenerate, the, absorbent by driving ofi" the acidic i'mpuritiesj Following removal of acidic con tituents; the gas is contacted with a second solution containing a moisture absorbent; under conditions suchthat; any carry-over of the acid gas absorbent from the first treating solution; is recovered together with absorbed moisture in the-second--solution. The latteris continuously circulatedthrough and regenerated in a second heating zone, from'which theevol ved" vapors are passed to the first heating zone for recovery ofthe acid gasabsorbent carryover" and its return'to-the-first mentioned treating Cycle. 7

It is found that regeneration of the second solution in the second heatingzone may result-in vaporization and carry over'ihto thefirst'heating zone, of quantities of *the moisture absorbent,- so that: int the course of extended operation the-sec: 0nd solution may become seriouslydepleted with respect-to the moisture absorbent; According-Ty; my primary object isto' replace-"themoi'sture ab sorbent. in the second: solution Samar its loss from the second heating-zone-isfully and: automatically madei-up'or compensated;

The present invention contemplates thezuse of a first treating-solution containing bothlaoidr' gas and moisture: absorbents; typical-131' any suitable amine such as, monoethanolamineg; and poly-=- h-ydric alcohol suchas diethylene glycol; lhe second. treating; solution willcontain: thesame glycol as: a, moisture: absorbent. Thuaregenera tion of the second solution mag-release toithe first heating, z0ne,. some vaporized glycol along, with the amine vapors. Suchdepletion otthesecnnd solution withlrespect to glycolis, compensated-by introducing a portion. or side streamlof. the first treating solution to: the. second soI'utiomat' aerate or in an amount which, may be automatically controlled in accordance with the required; glycol make-up. Preferably,, the make-up istakenas a side stream from the .leanfirst. solution ra- 6 Claims.

turned to the contactor,,. and; introduced: to the richisecond solution in or: flowing to the;- secondheating zone; all; under automatic; control; as will. later appear.

All, th i-varioue reatures, and, objects of the, inuention; as well. asrthe details or an illustrative embodiment, will berunderstoodto better advane ta/ge fromthe following detailed description of the, accompanying drawing which illustrates. the invention-in flow sheet-dorm.

} The hydrocarbon gas, to.- be; treated, containing moisture, and acidic: impurities; is introduced through: line; I In, to the. contactor column I I within which the; gas, rises, in intimate mixture with a. downfiowing, stream. of the; regenerated first solution) being: returned to the column through line L21 Typically thiesolution, may-contain 10 heating zone or still Illr whichmay consist ofthe usual stripping column equipped with the customary. bottom reboiler and its connectionswith thevcolurnnh all, as generally indicated. at 1.5-. The absorbed acidic impurities,.vaporized from the-soa result of heating. in the still, pass overhead, through line I Ii. to. the condenser I1, water, co'nd'ensata recovered invthe accumulator I18 being return, as, reflux to. the column through line I9: Thejlean or. regenerated-solution flows from the, base of: the, still: through line 2e, and exchanger, I3I"to be=re.turned by pump. 21 through line I2 and cooler 22 to thecontactor column I,.I

D'ehydi'at'ionof the, gas following removaLof its acidic impurities. in column I! ,.may take place at substantially the same pressure,,or at a. substantially higher pressure. In either case the. gas stream may carry over. smallamounts oi amine from the first treating solution, and which is: to be recovered in the moisture absorption stage. The latter employs: a second contactor column 231 or top section, of the column. Ir, and into which the gas passes through line 24 whichmay include'a compressor 2.5 when moisture absorp.-

is to occur at increased pressure. Typically the pressure in. column Iil' may be int-he. order of'150' pounds p. s. i'., and around 50.0. pounds p s. 'i'. in'the, second contacting, zone. 23... The gas" flows upwardly within the latter column. in contact with. an aqueous glycol, solution introduced" through line 26' and which, aitler absorption ofiflmoistine and, amine. carry-over from the gas /is withdrawn through line 21;. The. treated ga leave the columnthroughline 2'8jlf.,

The rich second solution is discharged through line 21 and exchanger 28 to a second heating zone or reboiler 29 wherein the solution is heated sufficiently to vaporize the absorbed moisture and amine which are removed through line 30 to the first heating zone l4 wherein the amine is recovered by condensation in the first treatingsolution. The lean second solution flows from reboiler 29 through line 3| to an accumulator 32 having a vapor pipe connection 33 with line 30. From the accumulator the solution-flows through line 34, exchanger 28 to be returned by pump 35 through line 26 and cooler 36 to the second stage contactor 23.

As previously indicated, the vapors leaving reboiler 29 through line 30 may contain small 4 gas absorbent and a small amount of the moisture absorbent, passing the resulting vapors into said first heating zone and therein recovering the vaporized acid gas absorbent and moisture absorbent, introducing to said second solution a sufiicient quantity of said firstsolution to compenises for; vaporization oflthe moisture j absorbent from said second heating zone,'and contactamounts of glycol which, though recovered in the 3 still I 4, deplete the second or moisture absorption solution to the extent of the carry-over. In accordance with the invention, a side stream of the first treating solution is added'to the second solution in such quantity or rate 'as may be required to makeup or compensate for the glycol carry-over from the still 29.

Preferably the make-up is taken from the lean first solution being returned from still 14 through lines 28 and E2 to the contactor II. For example, aside stream of' the lean first solution may be taken from line 28 in advance of the exchanger I31, through line 38 and into the rich second solution flowing through line 21 to the reboiler 29. The rate of make-up may be controlled by valve 39 actuated in accordance with the liquid level in accumulator 32, as by way of a liquid level controller conventionally indicated at 40 having an upper connection diagrammatically indicated by the dot-dash lineM, with the valve 39. Thus as the liquid level in accumulator 32 lowers as the glycol is depleted, valve 39 opens to admit a makeup side stream of the lean first treating solution. The amine content of the latter is at least'for the most part vaporized in the reboiler 29, and ultimately is recovered in still [4.

Instead of taking the make-upside stream at the location of line 38, the make-up may betaken from line I2 at the discharge side of pump 2 I, as through line 42 having a branch 43 connecting with line 27 in advance of the exchanger 28, and a second branch 44 connecting with line 38. Valve 45 is controlled through its connections 46 and H with thefloat control 40, to pass the required make-up to the secondsolution, in, the manner previously described with reference to valve 39. The described make-up lines may contain valves 47, 48 and 49 to permit flow of the solution into the second stage cycle through any of the indicated courses.

I claim:

1. The process of treating a gaseous mixture for the removal of moisture and an acidic compound, that includes contacting thegas with a first liquid solution comprising an acid gas absorbent and a moisture absorbent under conditions resulting in partial vaporization of the acid gas absorbent, then contactingfthe gas Witha second solution containing s'aidmoisture absorbent separable by fractionation from said acid gas absorbent and in which is absorbed moisture and the vaporized acid gas absorbent from said first solution, passing thespent first solution through a first heating zone to regenerate the first solution by vaporization of the absorbed acidic compound, passing the spent second solution through a second heating zone to regeneratethe second solution by vaporizing therefrom moisture, acid erated first and second solutions.

- 2. The process of treating a gaseous mixture for the removal of moisture and an acidic compound, that includes contacting the gas with a first liquid solution comprising an acid gas absorbent and a moisure absorbent under conditions resulting in partial vaporization of the acid gasabsorbent, then contacting the gas with a second solution containing said moisture absorbent separable by fractionation from said acid gas absorbent and in which is absorbedmoisture and the vaporized acid gas absorbent from said first solution, passing the spent first solution through a first heating zone to regeneratethe first solution by vaporizatio'n of the absorbed acidic compound, passing the spent second solution through a second heating'zone to regenerate the second solution by (vaporizing, therefrom moisture, acid gas absorbent and a small amount of the moistureabsorbent, passing the resulting vapors into said first heatingzone and therein recovering the vaporized acid gas absorbent and moisture absorbent, introducing to said second solution a sufiicient quantity ofthe regenerated first solution to compensate'for vaporization of the moisture absorbent from said second heating zone, and contacting gas to bevtreated successively with. the. regenerated first and second solutions. t

3. The process of treating a gaseous mixture or theremoval-of moisture and an acidic compound, that includes contacting the gas with a first liquid solution comprising an acid gas absorbent and a moisture absorbent under conditions resulting in partial vaporization of the acid gas, absorbent, then contacting the gas with'a second solution containing said moisture absorbentseparable by fractionation from said acid gas absorbent and in which is absorbed moisture andthe vaporized acid gas absorbent from said first solution, passing the spent first solution through a first heating zone to regenerate the first solution by vaporization of-the absorbed acidic compound, passing the spent second solution through a second heatingzone to regenerate the second solution by vaporizing therefrom moisture, acid gas 'absorbent'and a small amount of the moisture absorbent, passing'the resulting vapors into said first heating zone and therein. recovering the vaporized acid gas absorbent and moisture absorbent, introducing to the second solution flowing from said second heating zone a quantity of the lean first solution flowing from said first heating zone sufiicient to compensate for vaporization of the moisture absorbent from said second heating zone, and contacting gas to be treated successively with the regenerated first and second solutions. l

4. The process of treating a gaseous mixture for the removal of moisture and an acidic compound, that includes contacting the gas with a first soltuion of a glycol and amine acid gas absorbent under conditionslresulting in partial vaporizatio'n of the: amine, then contacting the 'gas with a glycol secondsolution inwhich is absor-bed moisture and the vaporized amine, passing the spent first solution through a first heating zone to regenerate the solution by vaporization of the absorbed acid compound, passing the spent second solution through a second heating zone to regenerate the second solution by vaporizing moisture, amine and some glycol therefrom, condensing the vaporized amine and glycol from the resulting vapors and recovering the condensed amine and glycol in said first heating zone, introducing to said second solution a suffi cient quantity of said first solution to compensate for vaporization of glycol from said second heating zone, and contacting gas to be treated successively with the regenerated amine and glycol absorbent.

5. The process of treating a gaseous mixture for the removal of moisture and an acidic compound, that includes contacting the gas with a first solution of a glycol and amine acid gas absorbent under conditions resulting in partial vaporization of the amine, then contacting the gas with a glycol second solution in which is absorbed moisture and the vaporized amine, passing the spent first solution through a first heating zone to regenerate the solution by vaporization of the absorbed acid compound, passing the spent second solution through a second heating zone to regenerate the second solution by vaporizing moisture, amine and some glycol therefrom, condensing the vaporized amine and glycol from the resulting vapors and recovering the condensed amine and glycol in said first heating zone, introducing to the spent second solution a suflicient quantity of the regenerated first solution to compensate for vaporization of glycol from said second heating zone, and contacting gas to be treated successively with the regenerated amine and glycol absorbents.

6. The process of treating a gaseous mixture for the removal of moisture and an acidic compound, that includes contacting the gas with a first solution of a glycol and amine acid gas absorbent under conditions resulting in partial vaporization of the amine, then contacting the gas with a glycol second solution in which is absorbed moisture and the vaporized amine, passing the spent first solution through a first heating zone to regenerate the solution by vaporization of the absorbed acid compound, passing the spent second solution through a second heating zone to regenerate the second solution by vaporizing moisture, amine and some glycol therefrom, condensing the vaporized amine and glycol from the resulting vapors and recovering the condensed amine and glycol in said first heating zone, introducing to a stream of the spent second solution flowing to the second heating zone a quantity of the regenerated first solution flowing from said first heating zone sufficient to compensate for vaporization of glycol from said second heating zone, and contacting gas to be treated successively with the regenerated amine and glycol absorbents.

WILLIAM F. CHAPIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS McCartney Jan. 27, 1948 

1. THE PROCESS OF TREATING A GASEOUS MIXTURE FOR THE REMOVAL OF MOISTURE AND AN ACIDIC COMPOUND, THAT INCLUDES CONTACTING THE GAS WITH A FIRST LIQUID SOLUTION COMPRISING AN ACID GAS ABSORBENT AND A MOISTURE ABSORBENT UNDER CONDITIONS RESULTING IN PARTIAL VAPORIZATION OF THE ACID GAS ABSORBENT, THEN CONTACTING THE GAS WITH A SECOND SOLUTION CONTAINING SAID MOISTURE ABSORBENT SEPARABLE BY FRACTIONATION FROM SAID ACID GAS ABSORBENT AND IN WHICH IS ABSORBED MOISTURE AND THE VAPORIZED ACID GAS ABSORBENT FROM SAID FIRST SOLUTION, PASSING THE SPENT FIRST SOLUTION THROUGH A FIRST HEATING ZONE TO REGENERATE THE FIRST SOLUTION BY VAPORIZATION OF THE ABSORBED ACIDIC COMPOUND, PASSING THE SPENT SECOND SOLUTION THROUGH 